Zihao Zhang1,2, Qi Yang3,4, Zhaoyang Fan3, Xianchang Zhang1,2, Yujiao Yang4, Jing An5, Zhentao Zuo1, and Rong Xue1,6
1State Key Laboratory of Brain and Cognitive Science, Beijing MR Center for Brain Research, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China, People's Republic of, 2Graduate School, University of Chinese Academy of Sciences, Beijing, China, People's Republic of, 3Biomedical Imaging Research Institute, Cedars-Sinai Medical Center, Los Angeles, CA, United States, 4Xuanwu Hospital, Beijing, China, People's Republic of, 5Siemens Shenzhen Magnetic Resonance Ltd., Shenzhen, China, People's Republic of, 6Beijing Institute for Brain Disorders, Beijing, China, People's Republic of
Synopsis
In this study, we improved TOF-MRA
and T1w-SPACE to a higher resolution for imaging perforating arteries and
intracranial vessel walls at 7T. With the combination of the two techniques, we
are for the first time able to depict the position of perforators and the vessel
wall lesion in patients with ICAD. Small changes within the vessel wall may be
revealed, and the certainty of the diagnosis may become better established,
enabling better therapeutic management.Purpose
Intracranial vessel wall and
its pathology can be depicted with 7T vessel wall magnetic resonance imaging. However,
no study has been performed to investigate the combination of perforating
artery imaging
1 and vessel wall imaging
2 in one image setting
at 7T. We attempted to assess perforating arteries and atherosclerotic lesions
using high-resolution TOF-MRA and whole brain vessel wall imaging, and to
evaluate the association between image findings and clinical courses of stroke.
Material
and Methods
14 volunteers and 6 patients with ICAD were
recruited in the IRB approved study with informed consent. The diagnosis of
ICAD was listed in Table 1. All the images were acquired on a whole-body 7T MR
system (Siemens Healthcare, Erlangen, Germany) equipped with a Nova 32-channel
head coil. All the patients underwent TOF-MRA, 3D T1-weighted (T1w) SPACE, 2D
T1w and T2-weighted (T2w) TSE imaging. Post-contrast T1w-SPACE was applied on
patient 6.
For TOF-MRA, the parameters
were optimized to visualize the perforators from MCA: FA=24°, TR=26ms, TE=15ms, voxel=0.25x0.25x0.25mm3,
FOV=210x164x32mm3, GRAPPA=3, time of acquisition (TA)=9:23min. An
inversion recovery (IR) prepared 3D-SPACE sequence was applied for T1w vessel
wall imaging: time of inversion (TI)=1100ms, TR=2100ms, TE=13ms, voxel=0.53x0.53x0.53mm3,
FOV=128x170x170mm3, GRAPPA=3, TA=10:22min. The same parameters were
used in post-contrast T1w-SPACE. In 2D vessel wall imaging, a multi-slice Turbo
Spin Echo (TSE) was positioned perpendicular to the MCA where the stenosis or
occlusion was observed in TOF-MRA or T1w-SPACE: TR=1800ms/TE=13ms for T1w, TR=3000ms/TE=52ms
for T2w, voxel=0.35x0.35x2.00mm3.
Results
In all the healthy volunteers,
the optimized high-resolution TOF-MRA managed to image perforating arteries
arising from MCA. A typical Maximal Intensity Projection (MIP) image is given
in Fig. 1. To evaluate the quality of T1w-SPACE in whole-brain vessel wall
imaging, the SNR and CNR of vessel walls are calculated in several main
intracranial arteries. The results are listed in Table 2. The typical images of
MCA and PCA are shown in Fig. 2, in which the profile of vessel wall is
illustrated.
The images of patient 2, 3 and 6 are presented here as
the examples in clinical scanning (respectively in Fig. 3, 4 and 5). In all the patients, TOF-MRA was able to visualize multiple perforators. The reconstruction
of 3D SPACE images was flexible to present the status of vessel wall in any
desired direction. The fusion of TOF-MRA and vessel wall images provided an
efficient way to estimate the risk of MCA stenosis or occlusion.
Discussion
The experiments on healthy volunteers ensured the performance of high-resolution TOF-MRA on the visualization of perforating arteries. In T1w-SPACE vessel wall imaging, the SNR and CNR of vessel walls were high enough for clinical diagnosis. The high resolution of isotropic 0.53mm produced sharp profiles in MCA and PCA, which was beneficial to identify vessel walls from the CSF surrounded. The low signal in the lumen indicated that the flow signal was well suppressed.
With the higher attainable SNR at 7 T, it became possible to perform isotropic high-resolution vessel wall imaging with a whole brain coverage. This made it possible to reconstruct each artery with a different course in different orientations. Besides, combining the imaging of perforating arteries and vessel wall allows to distinguish the subtypes of patients with ischemic stroke, such as TOAST classification. In the current study, both the plaques and perforators in symptomatic ICAD patients can be readily depicted. The developments and optimization of vessel wall imaging protocols at 7T may help us find disease-specific key imaging findings of the intracranial arterial walls in stroke patients.
Conclusion
We demonstrated that high-resolution
TOF-MRA for perforating artery imaging and T1w-SPACE for whole brain vessel wall imaging are feasible at 7T. With the use of
intracranial vessel wall imaging and the perforator artery imaging, small
changes within the vessel wall may be revealed, and the certainty of the
diagnosis may become better established, enabling better therapeutic
management.
Acknowledgements
The work is supported in part by Chinese MOST grant (2012CB825500), CAS
grants (XDB02010001 and XDB02050001), AHA-15SDG25710441
and NIH-NHLBI 2R01HL096119.References
1. Harada T, Sato Y, Nanba T, et al. High-Resolution MR Angiography at
7T: Detection of Perforating Arteries of the Anterior Communicating and Distal
Middle Cerebral Arteries. In: Proceedings of the 22th Annual Meeting of the
ISMRM, Milan, Italy. ; 2014. p. 1411.
2. Yang Q, Song H, Zhang H, Ling F, Chung Y-C, Zhang L, Fan Z, Liu X, Li
K, Li D. Intracranial Vessel Wall MR Registry. In: Proceedings of the 23th
Annual Meeting of the ISMRM, Toronto, Canada. ; 2015. p. 0664.